Learn about packages: PackagesPackages are collections of Assets to be shared and re-used in Unity. There are two types of packages supported in Unity: Asset packages and packages available through the Unity Package Manager (UPM). Packages available through the Unity Package Manager are a fundamental method of delivering Unity functionality. More infoSee in Glossary

Unity User Manual sections

All of the Unity Editor’s 2D-specific features including gameplay, spritesA 2D graphic objects. If you are used to working in 3D, Sprites are essentially just standard textures but there are special techniques for combining and managing sprite textures for efficiency and convenience during development. More infoSee in Glossary and physics.

The visual aspects of the Unity Editor including camerasA component which creates an image of a particular viewpoint in your scene. The output is either drawn to the screen or captured as a texture. More infoSee in Glossary and lighting.

Simulation of 3D motion, mass, gravity and collisionsA collision occurs when the physics engine detects that the colliders of two GameObjects make contact or overlap, when at least one has a rigidbody component and is in motion. More infoSee in Glossary.

Asset Store help - help on Asset StoreA growing library of free and commercial assets created by Unity and members of the community. Offers a wide variety of assets, from textures, models and animations to whole Project examples, tutorials and Editor extensions. More infoSee in Glossary content sharing.

Known issues

Is a feature not working as you expect it to? It might be an existing Known Issue. Please check using the Issue Tracker at issuetracker.unity3d.com.